AIX PPC JIT warning

[Jeff Clites]

Recently config/gen/platform/darwin/asm.s was added, containing 
Parrot_ppc_jit_restore_nonvolatile_registers(). Corresponding code also 
needs to be added to config/gen/platform/aix/asm.s -- Parrot should 
fail to link on AIX currently, without this. I didn't try to update the 
AIX asm.s myself, since I wasn't confident that I could do this 
correctly without having a way to test.

So, someone with AIX asm expertise, please take a look.
Thanks,
JEff